An electric power steering apparatus that energizes a steering mechanism of a vehicle by using a rotational torque of a motor as an assist torque, applies a driving force of the motor as the assist torque to a steering shaft or a rack shaft by means of a transmission mechanism such as gears or a belt through a reduction mechanism. In order to accurately generate the assist torque (steering assist torque), such a conventional electric power steering apparatus (EPS) performs a feedback control of a motor current. The feedback control adjusts a voltage supplied to the motor so that a difference between a current command value and the motor current becomes small, and the adjustment of the voltage applied to the motor is generally performed by an adjustment of a duty ratio of a pulse width modulation (PWM) control.
A general constitution of a conventional electric power steering apparatus will be described with reference to FIG. 1. As shown in FIG. 1, a column shaft (a steering shaft, handle shaft) 2 connected to a steering wheel (handle) 1, is connected to steered wheels 8L and 8R through reduction gears 3, universal joints 4a and 4b, a rack and pinion mechanism 5, and tie rods 6a and 6b, further via hub units 7a and 7b. Further, the column shaft 2 is provided with a torque sensor 10 for detecting a steering torque Th of the steering wheel 1, and a motor 20 for assisting the steering force of the steering wheel 1 is connected to the column shaft 2 through the reduction gears 3 (reduction ratio n). Electric power is supplied to a control unit (ECU) 30 for controlling the electric power steering apparatus from a battery 13, and an ignition key signal is inputted into the control unit 30 through an ignition key 11. The control unit 30 calculates a current command value of an assist (steering assist) command based on the steering torque Th detected by the torque sensor 10 and a vehicle speed Vel detected by a vehicle speed sensor 12, and controls a current supplied to the motor 20 based on a voltage command value Vref obtained by performing compensation and so on with respect to the current command value in a current control section. A steering angle sensor 14 is not indispensable and may not be provided.
A controller area network (CAN) 50 to send/receive various information and signals on the vehicle is connected to the control unit 30, and it is also possible to receive the vehicle speed Vel from the CAN 50. Further, a Non-CAN 51 is also possible to connect to the control unit 30, and the Non-CAN 51 sends and receives a communication, analogue/digital signals, electric wave or the like except for the CAN 50.
In such the electric power steering apparatus, there has been conventionally provided a VR-detecting circuit from a motor power-source circuit and a detecting circuit of a control voltage Vbat1 from a control power-source circuit, and an extraordinary (abnormal) state detection of a motor power-source voltage VR detecting circuit is performed by supervising a correlation between detected voltage values of the power-source voltage VR and the control voltage Vbat1. This is a method to utilize a fact that a correlation relation between the power-source voltage VR and the control voltage Vbat1 does not basically and greatly come off. As a prior art used such correlation relation, an extraordinary state detecting means is disclosed, for example, in Patent document 1 (Japanese Published Unexamined Patent Application No. 2009-161156).